WASHINGTON (CNN)— Taliban leader Mullah Akhtar Mohammad Mansour was killed in an airstrike Saturday in Pakistan, sources within al Qaeda and the Taliban, reached through an intermediary by CNN, confirmed Sunday.

A U.S. official said the drone strike occurred around 6 a.m. ET Saturday in a remote area of the Pakistan-Afghanistan border, southwest of the town of Ahmad Wal.

"Mansour played a key leadership role in not only orchestrating the Taliban but orchestrating a variety of other organizations to include the Haqqani Network and al Qaeda who were perpetrating operations against not only U.S. forces but coalition forces and Afghan forces for a long period of time," Gen. Joseph Votel of U.S. Central Command said at a news conference in Amman, Jordan. "He's an individual who has been in that structure for a long time. I'm glad he's gone."

U.S. Secretary of State John Kerry said Mansour "was directly opposed to peace negotiations."

"This action sends a clear message to the world that we will continue to stand with our Afghan partners as they work to build a more stable, united, secure and prosperous Afghanistan," Kerry said at a news conference in Myanmar. "It is time for Afghans to stop fighting and to start building a real future together."

The United States notified Pakistan's government of the strike, Kerry said.

"We have had longstanding conversations with Pakistan and Afghanistan about this objective with respect to Mullah Mansour, and both countries' leaders were notified of the airstrike," he said. "And it is important for people to understand that Mullah Mansour, as I said a moment ago, has been actively involved in planning attacks in Kabul, across Afghanistan, presenting a threat to Afghan civilians and to the coalition forces that are there."

Pakistan: Strike a violation of sovereignty

Pakistani officials said they were informed after the strike was carried out.

"While further investigations are being carried out, Pakistan wishes to once again state that the drone attack was a violation of its sovereignty, an issue which has been raised with the United States in the past as well," said a statement from Pakistan's Ministry of Foreign Affairs.

Mansour was the target of the strike, and a second adult male combatant traveling with him in a vehicle also was likely killed, the U.S. official said.

U.S. officials are still assessing the results, the official said. A second source, a senior administration official, said it would likely take days to get "physical confirmation" because of the remote location.

Afghan officials confirmed the killing.

Abdullah Abdullah, Afghanistan's chief executive, tweeted that Mansour was the victim of a drone strike that targeted his car in the Dahl Bandin area of Quetta in Pakistan.

Afghanistan's intelligence agency, the National Directorate of Security, also said Mansour was killed in an airstrike in Pakistan's Balochistan province.

The strike was carried out by multiple unmanned aircraft operated by U.S. Special Operations forces. There was no collateral damage, the first U.S. official added.

President Barack Obama authorized the strike.

Key figure in Taliban

The Pentagon confirmed the strike but didn't say whether Mansour was killed.

"Mansour has been the leader of the Taliban and actively involved with planning attacks against facilities in Kabul and across Afghanistan, presenting a threat to Afghan civilians and security forces, our personnel and coalition partners," Pentagon press secretary Peter Cook said in a statement.

"Mansour has been an obstacle to peace and reconciliation between the government of Afghanistan and the Taliban, prohibiting Taliban leaders from participating in peace talks with the Afghan government that could lead to an end to the conflict."

Sen. Lindsey Graham of South Carolina, one of the more hawkish Republicans in the Senate, welcomed the news and urged Obama not to withdraw troops from Afghanistan "until conditions on the ground permit their withdrawal."

"I'm glad to hear we decided to bring the leader of the Afghan Taliban, Mullah Akhtar Mansour, to justice. Mansour has terrorized the Afghan people as well as coalition forces," Graham said in a statement. "I appreciate President Obama for authorizing the attack. And job well done to the members of our military and intelligence communities who carried out the mission."

Sen. Bob Corker, a Tennessee Republican and chairman of the Senate Foreign Relations Committee, said, "If verified, the death of Taliban leader Mullah Akhtar Mansour would be an important victory in the fight against terror and welcome news to our military personnel in Afghanistan and the Afghan government."

Rise through the ranks

The Taliban revealed last year that Mansour assumed command following the death of longtime leader Mullah Mohammed Omar, who died in Pakistan in 2013.

Mansour formerly headed the leadership council of the Taliban and Islamic scholars, also known as the Quetta Shura, which includes longtime leaders who direct the Taliban's operations from Pakistan's Balochistan province, according to the Jamestown Foundation, a global research and analysis group.

According to the U.N. Security Council sanctions list, Mansour had been the Taliban's minister of civil aviation and transportation and was considered "a prominent member of the Taliban leadership."

"He was repatriated to Afghanistan in September 2006 following detention in Pakistan. He is involved in drug trafficking and was active in the provinces of Khost, Paktia and Paktika in Afghanistan as of May 2007. He was also the Taliban 'Governor' of Kandahar as of May 2007," the U.N. document said.

He was an active recruiter in the Taliban's fight against the Afghan government, the United Nations said.